A number of applications in the field of micro-electronics require structuring semiconductor substrates down to deep regions of the substrate. Examples of these applications can be found in the field of power electronics (high voltage components), the field of sensory devices, micro-electromechanical systems (MEMS), etc. The deep structuring of the semiconductor substrate is sometimes referred to as “3D Integration”. Creating cavities and/or recesses in the semiconductor substrate typically requires etching the substrate from one of its main surfaces, or depositing new matter on the main surface of the semiconductor substrate while masking the site or location of the future cavity or recess. Particularly when the cavities are obtained by means of an etching process, the dimensions of the cavities are subject to constraints imposed by the etching process. For example, the so-called “Deep Trench” etching process obeys a relatively fixed relation between a width of a trench to be etched and a depth of this trench. In cases where the closed cavity or a partly closed cavity is to be obtained within the substrate, the creation of a cover layer to close the cavity typically requires extensive manufacturing methods, due to the large dimensions of the cavities which cannot be closed with conventional semiconductor manufacturing technologies in a satisfactory manner.
The manufacturing of a pressure sensor shall illustrate the encountered problems in a representative manner for all types of applications requiring a similar 3D structuring of a semiconductor substrate. Pressure sensors are typically used to measure the pressure of a liquid or a gas, such as air. Pressure sensors typically provide an output signal that varies, based on the pressure sensed by the pressure sensor. One type of pressure sensor includes a standalone pressure sensor that is coupled to, or bonded to, a sensor surface, such as an application specific integrated circuit (ASIC). This type of pressure sensor is expensive to fabricate. Connecting this type of pressure sensor to a sensor circuit is also expensive. Another type of pressure sensor is a pressure capsule (e.g. a poly-silicon plate) that is integrated with a sensor circuit, such as an ASIC, during a back-end-of-line (BEOL) process. This type of pressure sensor is also expensive to produce, since several additional mask levels are required to fabricate the pressure sensor.
Semiconductor structures manufactured by 3D integration often require an electrical insulation between different parts of the semiconductor structure. This requires creating or providing an insulating region possibly deep within the semiconductor substrate so that conventional surface-oriented methods such as doping are unsuitable.